156-215.81.20 VPN Basics Practice Question
An administrator is configuring a VPN community in SmartConsole for a set of gateways that will use IKEv2. The administrator wants to ensure that the VPN tunnel can be established even if the two gateways are behind NAT devices. Which setting should be enabled in the VPN community?
⚠ Common exam trap
It's easy for candidates to confuse features that improve VPN performance or behavior (compression, permanent tunnels) with those that solve connectivity through NAT.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Enable NAT Traversal
NAT Traversal must be enabled to allow IPsec packets to pass through NAT devices by encapsulating them in UDP. Without it, NAT would modify the IP headers and likely cause the VPN tunnel to fail. Other settings like IP Compression, Aggressive Mode, or Permanent Tunnels do not solve NAT-related issues, so they are not correct for this scenario.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Support IP Compression
Why it's wrong here
IP Compression reduces the size of IP packets to improve throughput, but it does not help with NAT traversal. NAT devices may alter IP headers, and compression does not address that. Enabling IP compression is unrelated to establishing a tunnel through NAT. Therefore, this setting is not the correct choice for the scenario.
- ✗
Set Permanent Tunnels
Why it's wrong here
Permanent Tunnels keep the VPN tunnel up even when there is no traffic, which can be useful for monitoring or ensuring immediate connectivity. However, it does not help with NAT traversal. The tunnel might still fail to establish if NAT is present and NAT-T is not enabled. Thus, this setting does not address the requirement.
- ✗
Use Aggressive Mode
Why it's wrong here
Aggressive Mode is an IKE Phase 1 mode that reduces the number of messages exchanged, but it is less secure and does not solve NAT traversal issues. It is sometimes used in scenarios where the responder's IP is not fixed, but it does not handle NAT. Therefore, it is not the correct setting for enabling VPN through NAT.
- ✓
Enable NAT Traversal
Why this is correct
NAT Traversal (NAT-T) encapsulates IPsec packets in UDP, allowing them to pass through NAT devices. This is essential when gateways are behind NAT because NAT modifies IP addresses and ports, which can break IPsec. By enabling NAT Traversal in the VPN community, the gateways will detect NAT and use UDP encapsulation, ensuring the tunnel can be established. This directly addresses the requirement.
Visual reference
Quick reference
VPN Protocol Comparison
| Protocol | Port | Encryption | Authentication | Use Case |
|---|---|---|---|---|
| IKEv2 / IPsec | UDP 500 / 4500 | AES-256 | Certificates / PSK | Site-to-site & remote access |
| SSL / TLS VPN | TCP 443 | TLS 1.3 | Certificates / MFA | Clientless remote access |
| L2TP / IPsec | UDP 1701 | AES (IPsec) | PSK / Certificates | Legacy remote access |
| WireGuard | UDP 51820 | ChaCha20 | Public keys | Modern high-performance VPN |
| PPTP | TCP 1723 | MPPE (weak) | MS-CHAPv2 | Legacy — avoid in production |
PPTP is considered insecure. IKEv2/IPsec and SSL VPN are the current recommended options.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Check Point exam blueprint
This 156-215.81.20 practice question is part of Courseiva's free Check Point certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 156-215.81.20 exam.